H5N1 and H5N5 avian influenza: pandemic risk, species jump, and biosecurity in livestock farms
Highly pathogenic avian influenza (HPAI), of the H5N1 subtype , is an influenza virus that circulates mainly among wild birds and poultry . In recent years, moreover, this pathogen has made repeated “species jumps” towards mammals ,including cattle, domestic cats, and, in isolated cases, humans. In fact, the world’s first human case associated with the H5N5 subtype was documented in 2025-2026 . To date, however, the risk to the general population remains low, while the direct and concrete risk to the biosecurity of poultry farms stands out .
What is avian flu and why are we talking about it in 2026?
This year, the risks associated with avian influenza have been a recurring theme , given recent outbreaks and worrying signs of viral evolution . However, avian flu strains are not all the same, differing in their level of pathogenicity.
HPAI vs LPAI: high and low pathogenicity
Avian influenza viruses are classified based on the severity of the disease they cause in poultry: highly pathogenic strains (HPAI ) cause rapid and high mortality in flocks, while low pathogenic strains (LPAI) generally cause milder illnesses. Since 2020, in particular, the H5 2.3.4.4b clade has been circulating , causing unprecedented numbers of deaths among wild birds and poultry in Africa, Asia, Europe, and, since 2021-2022, the Americas .
H and N subtypes: how influenza A viruses are classified
Influenza A viruses are classified based on two surface proteins, hemagglutinin (H) and neuraminidase (N) : hence names such as H5N1 or H5N5. The H and N combinations can reassort with each other, giving rise, over time, to new subtypes with different characteristics in terms of transmissibility and pathogenicity .
The leap in species: from birds to mammals to humans
Spillover is the process that allows a viral agent to infect a host other than its usual one , crossing the species barrier. This can occur following mutations in the viral genome , which, in effect, favor adaptation . This mechanism is significantly facilitated by close contact between animals of different species and/or between animals and humans .
H5N1 in dairy cattle and cats: recent cases
Beginning in 2024, the H5N1 clade 2.3.4.4b virus spread to dairy cattle in the United States , with some farm workers in direct contact with infected animals becoming infected . Concurrently, cases have been documented in domestic cats, often linked to the consumption of raw food contaminated with the virus.
The first confirmed case of cat-to-human transmission (May 2026)
A study published by the CDC in the Morbidity and Mortality Weekly Report documented the first serological evidence of H5N1 transmission from an infected domestic cat to a veterinary professional, in Los Angeles County, between December 2024 and January 2025. The person involved, who tested positive for specific antibodies and remained asymptomatic ,had not worn adequate eye and respiratory protection during exposure. All the cats involved in the outbreak, among other things, had consumed raw milk and meat, which later tested positive for the virus.
H5N5 in humans: what we know about the new subtype
In November 2025, Washington State (USA) recorded the world’s first human case of HPAI A(H5N5) infection , in a domestic poultry farmer with pre-existing health conditions . The patient died on November 21, 2025, approximately 28 days after the onset of symptoms, from respiratory failure . Genetic sequencing by the CDC (November 20, 2025) confirmed that this was an A(H5N5) virus never previously identified in humans. Investigations of identified close contacts, however, showed no evidence of human-to-human transmission.
Why experts monitor pandemic risk
Each species jump represents an additional opportunity for the virus to adapt to a new host . For this reason, authorities maintain continuous surveillance for human cases of H5N1 and H5N5, although, to date, there is no evidence of efficient viral transmission from person to person.
How it spreads in farms
The entry and spread of avian influenza within farms is a current and significant problem . Below, we outline its mechanisms and consequences.
Transmission routes: contact, contamination and aerosols in confined spaces
In poultry farms, the virus spreads through direct contact with infected animals or their secretions; through indirect contamination (equipment, means of transport, personnel, clothing); and through airborne viral particles in confined spaces with high animal densities. The combination of crowding, limited air exchange, and contaminated organic material makes indoor farming environments a high-risk environment for viral spread.
Mortality and economic impact on the poultry sector
HPAI outbreaks cause high and rapid mortality in poultry, with mandatory culling in affected areas and a significant economic impact on farms , including direct costs (loss of animals, production shutdown) and indirect costs (trade restrictions, protection zone measures and surveillance).
Biosecurity: Preventing the entry and spread of the virus
Given current trends, it is appropriate to optimize prevention strategies through a desirable integrated approach . In this regard, there is no shortage of guidelines of national importance, which can be combined with additional strengthening solutions .
The biosecurity measures provided for by national legislation
In Italy, the application of biosecurity measures in poultry farms is governed by the Ministry of Health Decree of May 30, 2023 , which defines structural, management, and behavioral requirements to prevent the entry and spread of influenza viruses in poultry farms. The Ministry of Health also adopts a national surveillance plan each year , which includes checks on both farms and wild birds.
Monitoring viral load in the air of livestock farms
In addition to the physical barriers (fences, intrusion filters , filter zones) and operational protocols (clothing changes, equipment disinfection, access control) required by law, managing air quality within livestock buildings is an additional factor. To this end, cutting-edge solutions can be used, such as the devices developed by e4life and, in particular, the e4 life farm version , designed for livestock farms. By emitting electromagnetic waves at a specific frequency, the device neutralizes viral threats dispersed in bioaerosols , while remaining harmless to livestock and workers.
FAQ — Frequently Asked Questions
- Can H5N1 avian influenza spread to humans?
Yes, but in rare cases and generally following close contact with infected animals (poultry, dairy cattle, and in one documented case, even a domestic cat). Efficient person-to-person transmission has not been identified; the risk to the general population remains low according to the WHO and CDC.
- What is the H5N5 virus and why is it a concern?
H5N5 is a subtype of highly pathogenic avian influenza. The world’s first human case, unfortunately fatal, was recorded in Washington state (USA) in November 2025. This is a cause for concern because it represents another example of a species jump that needs to be monitored, even though there is currently no evidence of human-to-human transmission.
- Can bird flu become a pandemic?
At present, the risk is considered low, as efficient person-to-person transmission has not been documented for any of the H5 subtypes currently being monitored. Surveillance remains high, however, because every species jump presents an opportunity for the virus to adapt, which must be monitored.
- How is avian influenza transmitted in farms?
In farms, transmission occurs through direct contact with infected animals, indirect contamination via equipment, vehicles, and personnel, and, in high-density confined environments, also through airborne particles containing the virus.
- What are the mandatory biosecurity measures for poultry farms?
In Italy, the measures are defined by the Ministry of Health Decree of May 30, 2023 and include filter zones and access control, anti-intrusion fences , cleaning and disinfection of vehicles and equipment, controlled management of incoming animals, and health surveillance plans.
- Can the viral load in the air of a farm be reduced?
Air quality management, through controlled ventilation and, as a complementary measure, air treatment/inactivation technologies, can help reduce airborne viral loads in high-density livestock farming environments, always in conjunction with, and not as a replacement for, the biosecurity measures required by law.
